Remove short and proceed to

Table A-5. +20V Supply Troubleshooting (Cont’d)

Low output voltage	1.	Measure voltage at the	a.	Measured voltage is less than 0	a. Check for open Q9, Q6, R26, or
(lower than rating)		base of Q5.		volt.		CR5.
			b.	Measures voltage is more than 0	b.	Proceed to step (2).
				volt.
	2.	Eliminate current limit	a.	Output voltage increases.	a. Check for U6B defective.
		circuit as a source of	b.	Output voltage remains low.	b. Reconnect lead and proceed to
		trouble by disconnecting				step (3).
		anode of CR11.
	3.	Measure voltage at pin 3	a.	Measured voltage is near	a.	Check for defective U6A.
		of U6.		-0.7V.
			b.	Measured voltage is zero volt.	b. Check for CR14 or CR15 shorted.
					c. Check for open R39, shorted R36,
			c.	Measured voltage is near		or leaky or shorted C7.
				+0.7V.

		Table A-6. -20V Supply Troubleshooting

SYMPTOM		STEP - ACTION		RESPONSE		PROBABLE CAUSE

	The +20V supply must operate properly before troubleshooting the -20V supply.

High output voltage	1.	Attempt to turn off Q8 by	a.	Output voltage remains high.	a.	Q8 shorted.
(more than 1%		shorting emitter-to-base	b.	Output voltage becomes near zero	b.	Remove short and proceed to
greater than +20V		of Q8.		volt.		step (2).
supply in fixed
tracking ratio mode)	2.	Measure voltage at	a.	Measured voltage is more than	a. Check for open CR20 or R14 and
		base of Q7.		0 volt.		check for defective U8A.
			b.	Measured voltage is less than	b.	Check for defective Q7.
				0 volt.

Low output voltage	1.	Measure voltage at the	a.	Measured voltage is more than 0	a. Check for open Q8, Q3, and R24.
(more than 1% lower		base of Q7.		volt.	b.	Proceed to step (2).
than +20V supply in			b.	Measured voltage is less than
fixed tracking ratio			0	volt.
mode)					a. Check for U8B defective.
	2.	Eliminate current limit	a.	Output voltage increases.	b. Reconnect lead and proceed to
		circuit as a source of	b.	Output voltage remains low.		step (3).
		trouble by disconnecting
		anode of CR18.
					a. Check for defective U8A.
	3.	Measure voltage at pin 3	a.	Measured voltage is near
		of U8.		+0.7V.	b. Check for shorted CR21 and
			b.	Measured voltage is zero volt.		CR22.
					c. Check for open R15, shorted R41,
			c.	Measured voltage is near		or leaky or shorted C6.
				-0.7V.

A-9

SYMPTOM